Fix the logic of canceling previous scheduled fade in animation.

animateBoundsImpl() gets called twice when swiping up to home in
portrait mode (one time for initial pip, one time for replacing it above
shelf), while it only gets called once in other scenarios. The current
implementation assumes that it gets called twice, so it doesn't
correctly handle those one standalone call scenarios.

Test: Manual
Test: atest PinnedStackTests
Fixes: 133507275
Change-Id: I3df26ac8ed2c85ff4f1a8c4410a9a8a8f0d70f28